Electric discharge device



May 29, 1962 H. DE BoYNE KNIGHT 3,037,141

ELECTRIC DISCHARGE DEVICE Filed May 2, 1960 GHT y 19 /M/f/Wof? TTOPNEY /7f/VRY 'DE BOY/V- 3,037,141 Patented May 29, 1962 3,037,141 ELECTRIC DISCHARGE DEVICE Henry De Boyne Knight, Rugby, England, assigner to AS- sociated Electrical Industries Limited, London, England, a British company Filed May 2, 1960, Ser. No. 26,213 Claims priority, application Great Britain May 8, 1959 4 Claims. (Cl. 313-193) This invention relates to electric discharge devices of the kind in which the discharge has the characteristic of an arc, and occurs between an electron-emitting electrode and an anode in an envelope which contains an ionizable medium at a pressure, under operating conditions, which is generally not greater than two thousand microns of mercury. l In the specification accompanying prior U.S. application No. 839,937, led by me on September 14, 1959, and assigned to 'I'he British Thomson-Houston Co. Ltd., devices are described in which a low-pressure gas or vapour discharge is initiated on the path between an anode and an auxiliary thermionically-emiitting cathode and transfers to a path between the anode and an arc spot which forms on the main cathode, from which emission is of the cold cathode type. The transfer is encouraged by causing the initial discharge to pass through a restricting aperture in or adjacent to the main cathode and providing insulating members or particles in close relation to conducting members or particles on the main cathode adjacent to the aperture.

The formation of the arc spot on the main cathode and the resulting initiation of a discharge between anode and main cathode may, alternatively, -be induced by the production of a priming discharge from an auxiliary anode to the auxiliary cathode, as disclosed in U.S. application Serial No. 22,778, filed April 18, 1960, and assigned to the assignee of the present application. Control of the initiation of the priming discharge may be eifected by a grid member interposed in the priming discharge path.

In the device according to the present invention, there is provided, between the main cathode and the anode, at least one further cathode, on which the arc established between the main cathode and the anode may root so that the main discharge is then in the form of two or more arcs in series.

Preferably the, or each, further cathode is in the form of an aperture-d barrier member, near the rim of the aperture in which is material capable of readily forming an electron-emitting spot under the influence of the arc between the main cathode `and the anode. The, or each, further cathode may, as preferably does the main cathode, thus incorporate a body composed of an intimate association of metal conducting powder with powdered insulation as disclosed in the specification of the first abovementioned application.

Under some conditions of current and applied voltage the current from the anode to the main cathode may pass as a single arc, or, when two or more intermediate further cathodes are used, one or more may be passed-by by an arc; the invention thus provides that when this does not happen., the, or each, intermediate electrodes be suitable to act as a cathode emitting by cold cathode processes.

The invention will be more readily understood from a consideration of the accompanying drawings, in which FIG. l shows diagrammatically an electric arc discharge device embodying the features of the invention; FIG. 2 is a circuit diagram illustrating an arrangement in which the device of FIG. 1 may be utilised; and FIGS. 3, 4, and 5 illustrate constructions which may be used for the main and further electrodes.

The device illustrated in FIG. l employs only a single further cathode. In a vacuum envelope 1 are mounted an anode 2, a main cathode 3 and a further cathode 4, the envelope containing an atmosphere of a 10W pressure of gas and/or vapour. A quantity of mercury may be introduced into the envelope to provide such vapour. vThe cathodes 3, y4 consist of metal members 7, 8, respectively, furnished with one or more apertures 5, 6, which may be in line with the axis of the electrode structure, or may be out of alignment by any amount suited to the operating characteristics desired. Either or both of the cathodes 3, `4 may embody, as described above, means facilitating cathode spot formation. Cathodes 3, 4' are fixed to and electrically in contact with flanged Washers 7, 8 which substantially lill the cross-section of envelope 1, but allow space for the passage of liquid mercury 'should this be included from one end of the envelope to the other. Apertures in washers 7, y8 are aligned with apertures 5, 6 in the cathodes 3, 4.

Washer 7 is held by support lead 9 which is in contact with the lead 10 which passes through the envelope and functions as the main-cathode terminal. Washer 8 is welded to and supported by the lead 12 which, in turn, is 'supported by glass stem 13 sealed through a side-arm 14 of the envelope and which functions as the intermediate cathode terminal. Metal caps 11, 15, threaded over and welded to the leads 10, 412., respectively, screen the junctions between the leads and the glass beads 10A, 12A, added to the leads to facilitate their sealing to the envelope The anode 2 is supported by a lead 16 which is sealed through the glass and which `functions as the anode terminal. When high voltages are to be applied between the anode 'and the main cathode, the lead 16 may be supported by a yglass stem of any known design suited to high voltage operation.

A thermionically emitting auxiliary cathode 17, shown as of the directly heated type, and consisting of a helix of suitable metal, such as nickel, coated with material of low work function, such as the oxides of the alkaline earths, is connected to and supported by leads 18, 19. An auxiliary electrode in the form of a perforated transverse bale 20, fitted to a sheet-metal cylindrical member` 21 is held by support lead 22.

The operation of the device is illustrated by the circuit diagram of FIG. 2. The anode 2 and the main cathode 3 are connected to supply mains 31 in series with the load circuit 32. The further cathode 4i is connected to anode 2 by means of resistor 33 and to main cathode 3 by means of resistor 34; capacitors 35, 36 may be connected in parallel with resistors 33, 34 if desired.

The auxiliary electrode 20 is connected to the thermionic auxiliary cathode 17 by means of a control circuit `37, through which the potential of auxiliary electrode 20 with reference to auxiliary cathode 17 can be controlled at will. Auxiliary cathode 17 is also connected to main cathode 3 via resistor 38 and capacitor 3'9; in some cases it may be found sufficient for resistor 38 to consist of the leakage resistance, and the capacitor 39 to consist of the stray capacitance, between main cathode 3 and auxiliary cathode 17.

In operation, the potential of auxiliary electrode 20 `with respect to auxiliary cathode 17 is initially such that no discharge takes place to the auxiliary cathode l17; when this potential difference is changed suiciently in the positive direction, a discharge takes place to the auxiliary cathode 17, either from the electrode 20, or from the anode 2, or cathode 6, or from any other electrode (not shown in the diagram) at a suitable potential. Charged particles from this discharge are present in or iind their way in-to the aperture 5. Provided the potential of anode 2 is high enough, a discharge takes place between cathodes 4 and 3; charged particles associated with this discharge, passing through aperture 6, give rise to a discharge between cathode 4 and anode 2. `If the current in the discharge is high enough, cathode spots are formed on cathodes 3 and 4, the current passing between anode 2 and cathode 3 as two arcs in series.

The presence of the further cathode 4, at a potential intermediate between those of anode 2 and main cathode 3, increases the potential which can be applied between the latter electrodes without uncontrolled breakdown. Cathode 4 also serves as a deionizing baille at the end of current conduction.

The main and auxiliary cathodes `are shown and described in FIG. 1 as being of conducting material, e.g. graphite, nickel, molybdenum. Alternatively, as shown in FIG. 3, the members 3, 4 may consist, wholly as shown in FIG. 3, or in part as shown in FIG. 4, of a sintered mixture of conducting and insulating particles, e.g. nickel and alumina. If members 3, 4, consist in part only of such mixture, the part consisting of such mixture is located as shown in FIG. 4 in the vicinity of the apertures 5, 6. Alternatively, again as shown in FIG. 5, an insulating member 3a, 4a may be located in the neighbourhood of the aperture in close contact with the conducting members 3, 4, respectively, so as to encourage the formation of a cathode spot by field emission.

The thermionically-emitting cathode (shown as directly heated in FIGS. 1 and 2) may alternatively be indirectly heated, or be in the form of a pool type cathode.

What I cl-aim is:

l. An electric arc discharge device comprising a sealed envelope, an anode and an auxiliary electron-emitting cathode spaced apart in said envelope, an ionizable medium in said envelope capable of supporting an arc discharge between said auxiliary cathode and said anode, a main cathode located in the path of said arc discharge between said auxiliary cathode and said anode, and a further cathode located in said arc discharge path between said main cathode and said anode, said main and said further cathode each being constituted by a metal member extending transversely of said arc discharge path and having an -aperture therein with conducting material at the rim of each aperture, each metal member having insulating material in contact with said conducting material at the rim of said aperture therein.

2. An electric arc discharge device according to claim l and having an auxiliary electrode interposed in the path of the discharge between said main cathode and said auxiliary cathode to control the starting of said discharge.

3. An electric arc discharge device yaccording to claim 1, in which the apertures in said main and said further cathodes are in alignment in said arc path.

4. An electric arc discharge device according to claim l, in which the apertures in said main and said further cathodes are out of alignment with one another in said arc path.

References Cited in the le of this patent UNITED STATES PATENTS 2,409,855 Hillyer Oct. 22, 1946 2,514,165 Ramsay July 4, 1950 2,802,131 Meyer Aug. 6, 1957 2,805,353 Nienhuis Sept. 3, 1957 2,906,906 McCauley Sept. 29, 1959 2,948,825 Riley Aug. 9, 1960 

